Our understanding of ventricular function is based largely on studies of isolated papillary muscle. These studies have led to the concept that preload, afterload and contractility are the major determinants of ventricular performance. However, unlike isolated muscle systems, the ventricle has a complex three-dimensional structure. Normally the ventricle seems to exploit this three-dimensional structure by changing its shape from diastole to systole from a more spherical to less spherical shape which may contribute significantly to ejection of blood. This "shape change mechanism" may be analogous to gears that enable the same engine to perform quite differently depending on the needs of the operator. The ability of the heart to use this "shape change mechanism" is impaired in some disease states such as regional ischemia, right ventricular overloaded states, and cardiomyopathy. Until recently, we have had limited ability to study this "shape change mechanism" because our shape data has been limited to two-dimensional contrast ventriculograms or echocardiograms. We have developed a method by which 40-50 stainless steel beads can be implanted in the heart and the exact three-dimensional position of these beads determined from biplane radiographs. We have recently completed a new animal catheterization laboratory that allows us to obtain these films. With this technique we can now estimate deviation of the ventricle from a sphere, through the cardiac cycle and under a variety of loading conditions, both in normal and in disease states. We propose to use this technique to determine to what extent the ventricle uses its "shape change mechanism" in normal and disease states.